Various methods, systems and apparatus relating to the present invention are disclosed in the following co-pending applications filed by the applicant or assignee of the present invention simultaneously with the present application:
Each application is temporarily identified by its docket number. This will be replaced by the corresponding USSN when available.
This invention relates to a method of testing a micro electro-mechanical (MEM) device. The invention has application in ink ejection nozzles of the type that are fabricated by integrating the technologies applicable to micro electro-mechanical systems (MEMS) and complementary metal-oxide semiconductor (CMOS) integrated circuits, and the invention is hereinafter described in the context of that application. However, it will be understood that the invention does have broader application, to the testing of various types of MEM devices for various purposes.
A high speed pagewidth inkjet printer has recently been developed by the present Applicant. This typically employs in the order of 51200 inkjet nozzles to print on A4 size paper to provide photographic quality image printing at 1600 dpi. In order to achieve this nozzle density, the nozzles are fabricated by integrating MEMS-CMOS technology.
A difficulty that flows from the fabrication of such a printer is that there is no convenient way of ensuring that all nozzles that extend across the printhead or, indeed, that are located on a given chip will perform identically, and this problem is exacerbated when chips that are obtained from different wafers may need to be assembled into a given printhead. Also, having fabricated a complete printhead from a plurality of chips, it is difficult to determine the energy level required for actuating individual nozzles and for evaluating the continuing performance of a given nozzle.
The present invention may be defined broadly as providing a method of testing a micro electro-mechanical device of a type having a support structure, an actuating arm that is movable relative to the support structure under the influence of heat inducing current flow through the actuating arm, and a movement sensor associated with the actuating arm. The method comprises the steps of:
(a) passing at least one current pulse having a predetermined duration tp through the actuating arm, and
(b) detecting for a predetermined level of movement of the actuating arm.
The invention as above defined permits factory or in-use testing of the microelectro-mechanical (MEM) device, to determine whether the actuating arm is or is not functioning in the required manner to meet operating conditions. In the event that a predetermined level of movement of the actuating arm does not occur with passing of a current pulse having a predetermined duration, the device will be rejected or put aside for modification.
The testing method may be effected by passing a single current pulse having a predetermined duration tp through the actuating arm and detecting for the predetermined movement of the actuating arm. Alternatively, a series of current pulses of successively increasing duration tp may be passed through the actuating arm (so as to induce successively increasing degrees of movement of the actuating arm) over a time period t. Then detection will be made for a predetermined level of movement of the actuating arm within a predetermined time window tw where t greater than tW greater than tp.
The testing method of the invention preferably is employed in relation to an MEM device in the form of a liquid ejector and most preferably in the form of an ink ejection nozzle that is operable to eject an ink droplet upon actuation of the actuating arm. In this latter preferred form of the invention, the second end of the actuating arm preferably is coupled to an integrally formed paddle which is employed to displace ink from a chamber into which the actuating arm extends.
The actuating arm most preferably is formed from two similarly shaped arm portions which are interconnected in interlapping relationship. In this embodiment of the invention, a first of the arm portions is connected to a current supply and is arranged in use to be heated by the current pulse or pulses having duration tp. However, the second arm portion functions to restrain linear expansion of the actuating arm as a complete unit and heat induced elongation of the first arm portion causes bending to occur along the length of the actuating arm. Thus, the actuating arm is effectively caused to pivot with respect to the support structure with heating and cooling of the first portion of the actuating arm.
The invention will be more fully understood from the following description of a preferred embodiment of a testing method as applied to an inkjet nozzle as illustrated in the accompanying drawings.